Spontaneous intracerebral hemorrhage (ICH) comprises approximately 10% of all strokes with an annual incidence of approximately 15/100,000. Current treatment results are disappointing. Initial mortality remains high and survivors often have significant residual disability. New therapeutic approaches are difficult to pursue because little is known about the pathophysiologic mechanisms of brain injury. The goal of this research is to determine importance of cerebral ischemia as a mechanism of secondary tissue damage in human subjects with acute ICH. We will test the specific null hypothesis: Spontaneous supratentorial ICH does not produce regional cerebral ischemia potentially severe enough to cause tissue injury. We will perform this Specific Aim: We will measure regional cerebral blood flow (rCBF), regional cerebral metabolic rate of oxygen (rCMRO2), regional oxygen extraction fraction (rOEF) and regional cerebral venous oxygen content (rCvO2) using positron emission tomography (PE) in 60 patients with spontaneous supratentorial ICH. Initial measurements will be made within the first 24 hours and repeated 24-72 hours later. We will determine the proportion of patients with regional cerebral ischemia potentially severe enough to cause tissue injury and how this changes during the first few days after acute ICH. This research will provide fundamentally important pathophysiologic information about the possible role of ischemia in producing secondary brain injury in patients with ICH which will be of enormous value in planning future therapeutic investigations.